1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor device, a display device, a light-emitting device, a power storage device, a photoelectric conversion device, an imaging device, a driving method thereof, or a manufacturing method thereof. More particularly, the present invention relates to an imaging device including a scintillator.
2. Description of the Related Art
In medical practice, a medical diagnostic imaging device using X-ray film photography has been in wide use.
Since the imaging method using X-ray films involves a complicated management of the X-ray films, digitization of images is in progress. A known method for digitizing images uses an imaging plate. An imaging plate emits light when being irradiated with X-rays and the light is sensed with a scanner, so that digitized images can be obtained.
The imaging plate is a plate coated with a material (a photostimulable phosphor) emitting light by X-ray irradiation (this property is referred to as photostimulability) and has higher detection sensitivity to X-ray absorption difference than an X-ray film does. The imaging plate can be re-used because data of X-ray irradiation on the plate can be erased. However, the data that the imaging plate acquires is analog data, which needs to be digitized in a later process.
For this reason, in recent years, attention has been focused on flat panel detectors capable of acquiring digital data directly (e.g., Patent Documents 1 and 2). Flat panel detectors have direct and indirect conversion systems. In the direct conversion system, X-rays are directly converted into electrical charges with the use of an X-ray detecting element. In the indirect conversion system, X-rays are converted into visible light with a scintillator and the light is converted into electrical charges by a photodiode. In either system, a flat panel detector includes a plurality of pixel circuits arranged in a matrix.